Process for generating milk froth from milk powder and milk froth generating device and coffee machine suitable for performing this process

ABSTRACT

Milk froth generating device for generating milk froth from milk powder ( 7 ) and hot water comprises a hot water supply and a water heater. For simply obtaining milk froth of high quality, the milk froth generating device comprises a substantially rotation-symmetrical hot water sprayer head having hot water channels ( 9, 12 ) downwardly directed and open at the bottom. Some of them are disposed close to an outer convex surface ( 10 ) of the hot water sprayer head and some extending close to a central axis of the hot water sprayer head ( 1 ). The hot water channels are connected via a hot water distribution chamber ( 16 ) in the hot water sprayer head, and the hot water supply ( 17 ) with a hot water pressure generator and the water heater.

The present invention relates to a process for generating milk frothfrom milk power and hot water using a milk froth generating device as inaccordance with the preamble of claim 1.

Correspondingly, one aspect of the invention relates to a milk frothgenerating device as in accordance with the preamble of claim 2. Bymeans of this milk froth generating device, the process according toclaim 1 is to be carried out.

In the present application, the term milk froth refers to froth onbeverages wherein the froth consists of either milk or milky components,such as for instance froth of cocoa-containing beverages.

A further aspect of the present invention relates to a coffee machine,particularly an espresso machine comprising a hot water generator, a hotwater pump and a milk froth generating device to carry out the processaccording to claim 3. The term espresso machine will in the following beincluded in the term coffee machine.

For frothing up milk to prepare a cappuccino, the espresso machines arein most cases provided with steam nozzles. For the generation of milkfroth, the outlet of the steam nozzle is guided manually over thesurface of milk prepared in a vessel so that when releasing the steam, athree-phase zone comprising steam-air-milk is formed generating the milkfroth. In most cases, this process can optimally be mastered byprofessional users only.

For this reason, so-called frothing aids have been developed wherein thesteam outlet is simply submerged under the surface of the milk, and bymeans of a Venturi tube provided in the frothing aid via an air supplyduct remaining above the milk surface, air is drawn in the steam outletby the under pressure generated by the flowing steam so that thethree-phase zone is formed under the milk surface and frothing of milkis thus also made possible for users having no practice.

It is a disadvantage of the two methods that both the simple steamnozzles and the frothing aids will be heated in view of the passing hotsteam that much that milk remains may stick to the parts of the nozzlein contact with the milk and may even get burned. In case of simplesteam nozzles, this contact occurs because when the milk froth is beinggenerated, the three-phase zone is increasingly below the frothing foamand the milk froth will, therefore, stick to the nozzle. In the case ofthe frothing aids, sticking together is caused by the system consideringthat the frothing aids are submerged in the milk. In both cases, thesoiled parts of the device have to be thoroughly cleaned after use.While nozzles made of poorly heat conducting material might makeimprovements possible by a smaller tendency to sticking, they do not,however, solve the soiling and cleaning problem.

One cleaning problem is also observed in case of prior art milk frothingsystems where by means of the passing steam milk is drawn via a hoseduct from a container into a frothing chamber in which it is frothed upand continues to flow directly into the drinking cup. In these systems,hose supply ducts and frothing system have to be thoroughly rinsed withwater in order to avoid soiling by milk remains.

Milk froth generation from fresh milk causes a further problem. On onehand, the fat content of the milk determines the quality of the milkfroth being made as to pore size and stability, and on the other, themilk should be relatively cold. The keeping of defined fat contentlimits and temperature limits of the milk is therefore of significancefor the frothing result. A further disadvantage of milk froth generationbased on cold fresh milk results from the fact that while the hot steamwarms during the course of the generation of the milk froth theremaining milk in the frothing vessel, the remaining milk which in mostcases, for instance in case of a cappuccino, is added to the coffee inaddition to the milk froth displayed on the coffee will not reach thecoffee temperature and will, therefore, cool down the coffee, which ishighly undesired.

The state of the art includes also a milk froth generating device of ahouse hold coffee machine by means of which milk frothing should besimplified by using the steam supply duct of the coffee machine (EP-A-0509 505). The milk froth generating device comprises a laminarizationcone solidly affixed to the steam supply duct under discharge openingsat the otherwise closed end of the steam supply duct. The dischargeopenings are aligned, or inclined, so that the discharged steam jets areguided along the outer surface of the laminarization cone therebydragging air for the frothing effect along, whereby a laminar flow ofthe steam is generated on the cone surface in order to improve thepenetration of the steam jets into the milk and whereby in the milk intowhich the laminarization cone is partly submerged a turbulence isgenerated in order to improve frothing of the milk. This milk frothgenerating device has the above-described cleaning problem since thelaminarization cone has to be submerged in the milk. The laminarizationcone, furthermore, has to solve two contrasting partial tasks, namelydragging air along to perform the frothing effect and generatingturbulence in the milk, on one hand, and to partly laminarize the steamjets for a deep penetration into the milk, on the other. For thepreparation of hot beverages of instant powder, this prior art devicehas proved to be unsuitable.

The state of the art known from practice includes, furthermore, beveragepreparing and vending machines where a vessel is provided into which,first, milk powder is dosed in and afterwards hot water essentiallyunder atmospheric pressure is introduced whereupon, subsequently, themilk powder is dissolved by means of a machine-powered whisk, and bysimultaneous intermixing ambient air milk froth is generated from it.Thereafter, the whisk can be taken from the vessel to be rinsed andespresso, or coffee, can be introduced below the froth to make thebeverage ready. This milk froth generation is awkward particularly witha view to the required cleaning of the whisk, and the device to be usedfor performing the process is mechanically complicated.

It is the object of the present invention to provide an improved processfor generating milk froth from milk powder and hot water by which milkfroth of high quality is generated simply in one operation without usingfresh milk and rinsing or cleaning processes can be reduced.

A milk froth generating device suited for performing the process shouldneed little maintenance and should be reliable, and to this end shouldbe assembled by as few movable parts as possible.

This problem can, as in accordance with claim 1, be surprisingly simplybe solved in that the milk froth is generated from milk powder which istreated with hot water jets which under sufficient hot water pressureflow out pointedly from the milk froth generating device. The hot waterpressure is sufficient when it has the altitude typical for espressomachines which is either generated by a water pump with a followingcontinuous-flow heater or by a hot water boiler from which heated wateris discharged by steam pressure. By the water jets discharged under suchpressure, the milk powder accumulated and dosed for milk frothpreparation of one beverage portion in a frothing vessel is rapidlypenetrated and dissolved whereby under the inclusion of air milk frothwill almost instantaneously be generated. By means of the hot waterjets, sufficient kinetic energy can, therefore, be introduced into theaccumulated milk powder to perform the functions referred to abovewithout undesirably blowing the accumulated milk powder partly away ordamaging it by a too-high temperature.

A milk froth generating device according to the invention suited forperforming this process comprises a substantially axially symmetricalhot water sprayer head having hot water channels which are defined indetail according to claim 2 and provide for a uniform distribution ofthe hot water jets discharged from them. On the outside, the hot watersprayer head may be shaped to be favorable in production anduser-friendly, substantially cylindrical or as a truncated cone. Themilk froth generating device includes in addition to a hot water heater,a hot water pressure generator in connection via a hot water duct withthe hot water sprayer head.

According to claim 4, the functions of water heating and hot waterpressure generation or increase, respectively, may through the use of awater pump before a water heater, which in this case may be a simplecontinuous flow heater, be separated which makes constant hot waterpressure possible. Instead, these function may, however, also becombined in a water boiler which does not only heat the water butdischarges it also under hot water or vapor pressure.

Of particular advantage is an integration of the milk froth generatingdevice of the invention with a coffee machine, particularly an espressomachine according to claim 3, since in this case the water heatersthereof and the hot water pressure generators thereof may be used forthe generation of milk froth from milk powder according to the processof the present invention without, surprisingly, requiring differentdimensioning particularly of the hot water pressure generator.

In order to generate milk froth by using a coffee machine, particularlyan espresso machine, according to claim 3, which provides the hot waterunder pressure for frothing, and by using milk powder instead of milk asotherwise common with coffee machines and espresso machines, a definedamount of milk powder is, first, filled into a vessel open on topwhereupon the latter is put under the hot water sprayer head of the milkfroth generating device so that the milk powder is disposed spaced underthe hot water sprayer head. Subsequently, hot water supply to the hotwater sprayer head may be initiated. The hot water flowing into the hotwater sprayer head emerges from it under high pressure and following theconfiguration of the hot water channels in the hot water sprayer head isflushed over the milk powder and, by its kinetic energy, also into themilk powder. The milk powder is thus uniformly and rapidly dissolved sothat it gets into a state in which milk froth generation is increasinglyperformed. For the milk froth generation, the hot water jets flowingfrom the hot water channels have such a velocity that air is draggedalong, and they have that much kinetic energy that when impinging ontothe milk being formed in the vessel they will immediately froth it up.To this end, the hot water sprayer head is aligned so that it is alwaysabove the froth being formed and thus remains substantially free fromsoiling through milk remains. By constant composition of the milk powderand of the temperature exactly controlled in coffee machines and of theprescribed pressure of the hot water, milk froth generation of uniformlygood quality is assured. An additional advantage consists in thatcappuccino to which milk froth is added generated according to thisprocess from the frothing vessel will not cool down when simultaneouslyadding residual milk.

Suitable embodiments of the milk froth generating device according tothe invention and thus of the coffee machine in which it is employed aregiven in claims 4 through 18.

To uniformly distribute the hot water jets on the milk powderaccumulated in a frothing vessel, it has proved to be very suitablewhen, according to claim 6, near the outer convex surface of the hotwater sprayer head, about 10 hot water channels are disposedcircumferentially spaced uniformly relative to each other and, close tothe central axis of the hot water sprayer head, 3 to 4 hot waterchannels are disposed circumferentially spaced uniformly relative toeach other.

A considerable improvement of milk froth generation from milk power isobtained, according to claim 7, by a defined sloping arrangement of thehot water channels provided close to the outer shall surface of the hotwater sprayer head. Trials have shown that an inclination of the hotwater channels disposed closed to the outer convex surface about 2 to12° relative to the perpendicular is suitable, whereby it is sufficient,as according to claim 8, that only one lower section each of such hotwater channel is inclined while the section above it which provides forthe connection to the hot water supply, may be straight vertical

According to claim 9, the hot water channels disposed close to the outerconvex surface may, favorable for the production, generally be inclinedrelative to the perpendicular in the way referred to, i.e. about 2 to12° relative to the perpendicular

In the case of the above alternative embodiments of the hot waterchannels disposed close to the outer convex surface, it is essentialthat the outer hot water jets come out from them corresponding to thesloping hot water channel path, at least in the lower sections thereofwith a twist in circumferential direction of the hot water sprayer headand impinge with the twist on the milk powder. This promotes bothintimate mixing of the powder with the hot water and almost simultaneousfrothing. The water jets coming out near the central axis of the hotwater head, on the other hand, may, corresponding to the vertical pathof the hot water channels disposed in this area of the hot water sprayerhead, come out perpendicularly and impinge on the milk powder since theyare almost extensively screened by a curtain of the hot water jetsflowing with a twist from the outer hot water channels from the outersurrounding. The very effective sprayer head may compactly be madehaving for instance an outer diameter of 20 mm, the dimensions of thesprayer head being uncritical.

Structurally, and of advantage for uniform hot water jet configuration,the hot water sprayer head of the coffee machine is designed to includea cylindrical inner body and a pot-shaped outer body enclosing the innerbody. From the outer convex surface of the cylindrical inner body thehot water channels are essentially formed as laterally open hot waterchannels or slits. The hot water channels are completed by an innerconvex surface of the pot-shaped outer body slipped over the inner body,which laterally screens tightly the hot water channels. The screened hotwater channel slits in the shall surface of the inner body may in caseof rectangular cross sectional areas for instance be 0.2 mm wide and 0.2mm deep. Differently shaped cross sections having identical or similarpassage surfaces, however, are possible as well.

The hot water channels perpendicularly disposed close to the centralaxis of the hot water sprayer head may consist of cylindrical holeswhich are simply produced, for instance by drilling and may have aboutthe same passage surfaces as the outer hot water channels.

To assure that all hot water channels are evenly filled with the hotwater fed via the hot water supply duct, the hot water sprayer headsuitably includes, according to claim 10, a hot water distributionchamber which is left free between one upper side of the outer body andan upper side of the inner body and into which opens the hot watersupply duct. In this way, the individual hot water channels are evenlysupplied with the hot water via the hot water distribution chamber.

In the present description, the hot water channels essentially shapedout from the outer convex surface of the inner body are also referred toas outer hot water channels, and hot water channels formed as boresclose to the central axis of the inner body are also referred to asinner hot water channels.

In the embodiment of the hot water sprayer head according to claim 11,the inner body, and therefore also the ring covering it, in some caseswith the exception of a section serving the fixation of the inner bodyin the ring, broadens downwardly in a truncated cone-shaped manner. Inaddition, the outer hot water channels are in this case, also relativeto the imaginary central axis of the hot water sprayer head, not onlysloped in circumferential direction but also radially. Correspondingly,the outer hot water jets from the hot water sprayer head do not onlyspout sloping relative to the vertical in circumferential direction butalso downwardly broadened in radial direction. In this way, a largerportion, or surface, respectively, of milk powder can be treated withthe hot water jets. Here, the inner hot water jets may also spoutperpendicularly, as in the embodiment with the cylindrical inner body.

The substantially truncated cone-shaped inner body and the outer bodycovering it with a ring section, each, may include, according to claim12, an upper cylindrical section serving for fixing, easily removable ifnecessary, the inner body in the outer body, said upper cylindricalsection being provided with fixing elements, particularly a thread whichis shaped in the inner body as an external thread penetrated by sectionsof the hot water channel slits.

Instead of the cylindrical section, the truncated cone-shaped inner bodymay include for an unthreaded connection, according to claim 13, a bandwhich fits into an inner ring groove in the truncated cone-shaped ringinto which the inner body can be inserted. The inner body and/or thering are to this end made of elastic material such as Neoprene so thatthe ring is force-lockingly, though manually releasably, supported.

In the hot water sprayer head, between the hot water distributionchamber and the hot water channels, there is advantageously provided,according to claim 14, a sieve in order to avid clogging of the hotwater channels having small free cross sections by small particles thatare fed in together with the hot water. The sieve is correspondinglyfine-meshed.

According to claim 15, the sieve can suitably be supported by a spacerformed from the upper side of the inner body, which spacer might be adistance ring formed-out between the arrangement of the hot waterchannels in the outer convex surface of the inner body and thearrangement of the hot water channels close to the central axis.

For an easy assembly of the sieve and in order to provide the interiorof the hot water sprayer head accessible for maintenance, particularlycleaning, the features according to claim 16 advantageously provide thatthe pot-shaped outer body consists of an upper part and a cylindricalring screwed into it which is solidly connected with the cylindricalinner body, while from the upper part the inside flange is formed whichincludes an external thread so that it can be screwed to an internalthread in the upper section of the cylindrical ring. For maintenance,particularly for cleaning the sieve, the cylindrical ring may togetherwith the inner part simply be screwed off from the upper part so thatthe sieve and the hot water distribution chamber are completely exposed.In the screwed-together state, the interior space and the hot waterdistribution chamber are suitably sealed to the outside, according toclaim 17, by a sealing ring between the upper part and the cylindricalring. The opening possibility for maintenance is also made possible,according to claim 13 in the case of the substantially truncatedcone-shaped inner body and the ring.

In order to exclude scalding of the operator of the milk frothgenerating device even if he or she is unskillful or inattentive, thefroth generating device consists preferably of poorly thermo-conductivematerial.

Exemplified embodiments of the invention will in the following bedescribed based on a drawing including six figures from which furtherdetails and advantageous features of the invention will be come apparentand wherein

FIG. 1 shows in a diagrammatic perspective illustration a coffee machineincluding a milk froth generating device in operation,

FIG. 2 shows a hot water sprayer head including hot water supply duct,shown in broken lines, over a frothing vessel containing milk powder inworking position and in function,

FIG. 3 shows an underside of the hot water sprayer head,

FIG. 4 shows a lateral view, partly in cross section, through a firstembodiment of the hot water sprayer head,

FIG. 5 shows a lateral view, partly in cross section, through a secondembodiment of the hot water sprayer head, and

FIG. 6 shows a lateral view, partly in cross section, through a third,preferred, embodiment of the hot water sprayer head.

In all the figures, corresponding parts are given identical referencenumerals.

In FIGS. 2 through 6, each, it is only the hot water sprayer head of themilk froth generating device which is shown, not, however, the hot waterpressure generator in combination with a water heater in connection withthe hot water sprayer head, both belonging to a common coffee machine,particularly an espresso machine.

FIG. 1 shows diagrammatically a coffee machine of common structurecomprising a, not visible, water heater and a hot water pressuregenerator. On one front side 27, operating knobs for switching on P andfor preparing espresso E and cappuccino C can be seen. Outlet tubes 28for espresso and a hot water sprayer head 1 for milk froth preparationof the milk froth extend from the front side.

Using the coffee machine, by activating hot water sprayer head 1 a in afrothing vessel 2 disposed on a base 2 a of the coffee machine, milkfroth can be generated as will further below be explained and the milkfroth can subsequently be brought together with espresso or coffee thathas been prepared by the same machine.

FIG. 2 shows how hot water sprayer head 1 a for preparing milk froth isarranged above a portion of milk powder 7 placed in a frothing vessel 2.Hot water sprayer head 1 a is disposed spaced above milk powder 7. Via ahot water supply 17, hot water sprayer head 1 a receives hot water underhigh pressure from the water heater and the hot water pressure generatorof the coffee machine. From FIG. 2, it can be taken how outer water jets1 a, 1 b and inner water jets 6 coming from hot water sprayer head 1 aimpinge, approximately uniformly distributed, onto the portion of milkpowder 7 in order to dissolve it and to convert it for the greatestpart, under the inclusion of air dragged along by the inner water jetsand the outer water jets, to milk froth.

The configuration, particularly the even distribution of outer waterjets 4 a, 4 b and inner water jets 6 results from the arrangement of hotwater channels in hot water sprayer head 1 a from the open sides ofwhich they come out. As concerns the arrangement of the hot waterchannels, reference is made, to start with, to the simplest firstembodiment of hot water sprayer head 1 shown in FIGS. 3 and 4, and,subsequently, the second embodiment of hot water sprayer head 1 aaccording to FIGS. 1, 2, 5 will be dealt with. The underside of hotwater sprayer head 1 a, apart from possible dimensioning differences, isidentical to the underside of hot water sprayer head 1 shown in FIG. 3from which open sides of hot water channels 9, 12 can be taken.

FIG. 3 deals with inner hot water channels 12 designed as bores anddisposed close to a non-designated central axis on an imaginary innercircle 5, and with hot water channels 9 having rectangle-shaped crosssection formed out in a convex surface 3 of the inner body. As can betaken from FIG. 3, the outer hot water channels 9 are uniformly spacedin circumferential direction of convex surface 3. The inner hot waterchannels 12, too, are uniformly spaced relative to each other on theimaginary circle 5 in circumferential direction.

In the first embodiment of hot water sprayer head 1, hot water channels9 which constitute substantially hot water channel slits of uniformdepth formed in cylindrical inner body 8 on the convex surface 3thereof, compare also FIG. 4, are inclined towards the perpendicular incircumferential direction over the complete height of the cylindricalinner body.

The inner hot water channels 12 designed as bores, on the other hand,extend in all embodiments of the how water sprayer head non-inclined andperpendicular.

From FIG. 4, it can furthermore be taken how an outer body generallydesignated by reference numeral 11 encompasses cylindrical ring 20 whichincludes at the upper part thereof an internal thread 22 and encompassesupper part 21 from which projects downwardly an internal flange 23having an external thread which engages in internal thread 22 to keepupper part 21 screwed to cylindrical ring 20. The interior space therebyformed, substantially a hot water distribution chamber 16, is sealed bymeans of a sealing ring 21 in the area of the screw coupling. Hot watersupply 17 opens into the hot water distribution chamber defined above byupper part 21.

On one upper side 13 of cylindrical inner body 8, a distance ring 24 isformed out, as can furthermore be taken from FIG. 4, on which a sieve 19is disposed. The sieve is kept between distance ring 24 and internalflange 23 of the upper part.

The second embodiment according to FIG. 5 differs from the firstembodiment according to FIGS. 3 and 4 essentially in that outer hotwater channels 9 a do not extend over the total length thereof, inclinedrelative to the vertical in circumferential direction, in the lowersections thereof, however, they do. The outer hot water channels 9 a, inaddition, are radially inclined also relative to the central axis notshown of hot water sprayer head 1 a since the lower part of inner body 8a is bell-shaped or truncated cone-shaped, respectively.

The outer hot water jets 4 a, 4 b from hot water sprayer head 1 a ofFIG. 2, correspondingly, do not on extend in an inclined manner relativeto the vertical in peripheral direction but also downwardly enlarged inradial direction and impinge inclinedly on milk powder 7. In view of theenlargement of the outer hot water jets, a large portion, or surface,respectively, of milk powder can be treated with the hot water jets fromthe compact hot water sprayer head 1 a. The inner hot water jets may inthis case, as in the case of the first embodiment, flow perpendicularlyas well.

The third embodiment, according to FIG. 6, of hot water sprayer head 1 bdiffers from the second embodiment according to FIG. 5 in that the thirdembodiment includes an integral outer body 11 a consisting of upper partsection 21 a and a substantially bell-shaped ring section 20 b, an innerbody 8 b having an exterior thread 29 at its upper section being screwedinto an internal thread 30 of outer body 11 a. Hot water sprayer head 1b, can, therefore, easily be opened for maintenance purposes, to whichend a coin slit 31 is provided, and closed at the end. Hot water channelslits 9 b in the convex of inner body 8 b are essentially designed asare hot water channel slits 9 a of the second embodiment and penetratewith upper sections thereof throughout internal thread 30. To hold sieve19 to an inner edge, at the bottom of a hot water distribution chamber16 a peripheral projections 24 b are provided formed out above from theinner body.

1. Process for generating milk froth from milk powder (7) and hot waterby means of a milk froth generating device, characterized in that saidmilk powder (7) is treated with hot water jets (4 a, 4 b, 6) which flowout at substantially even distribution under hot water pressure fromsaid milk froth generating device.
 2. Milk froth generating device forgenerating milk froth from milk powder (7) and hot water comprising ahot water supply and a water heater, characterized in that said milkfroth generating device comprises a substantially rotation-symmetricalhot water sprayer head (1, 1 a, 1 b) having hot water channels (9, 9 a,9 b, 12) downwardly directed and open at the bottom, some of which beingdisposed close to an outer convex surface of said hot water sprayer headand some extending close to a central axis of said hot water sprayerhead, and that said hot water channels are connected via a hot waterdistribution chamber (16, 16 a) in said hot water sprayer head, and saidhot water supply (17) with a hot water pressure generator and said waterheater.
 3. Milk froth generating device according to claim 2,characterized in that said hot water pressure generator includes a waterpump.
 4. Milk froth generating device according to claim 2,characterized in that said hot water pressure generator and said waterheater are integrated in a water boiler according to the steam-pressureprinciple.
 5. Milk froth generating device according to claim 2,characterized in that close to the outer convex surface of said hotwater sprayer head (1, 1 a,1 b) about 10 hot water channels (9, 9 a, 9b) are disposed at peripheral distances identical relative to eachother, and close to the central axis of the hot water sprayer head, 3 to4 hot water channels (12) are arranged in peripheral distances identicalrelative to each other.
 6. Milk froth generating device according toclaim 2, characterized in that at least one lower section each of saidhot water channels (9, 9 a, 9 b) disposed close to the outer convexsurface is inclined relative to the perpendicular in peripheraldirection about 2 to 12° and that said hot water channels (12) disposedclose to the central axis of said hot water sprayer head extend inparallel to the central axis.
 7. Milk froth generating device accordingto claim 6, characterized in that only one lower section each of saidhot water channels (9 a, 9 b) disposed close to outer convex surfaces isinclined about 2 to 12° relative to the perpendicular.
 8. Milk frothgenerating device according to claim 6, characterized in that said hotwater channels (9) disposed close to the outer convex surface areinclined over the whole length relative to the perpendicular about 2 to12°.
 9. Milk froth generating device according to claim 2, characterizedin that said hot water sprayer head (1, 1 a) has a substantiallycylindrical inner body (8, 8 a, 8 b) in the outer convex surface ofwhich laterally open hot water channel slits are formed out, and whichincludes bores extending close to the central axis as hot water channels(12), that over the cylindrical inner body an essentially cylindricalring (20, 20 a), or ring section (20 b), respectively, is slipped whichlaterally covers tightly said hot water channel slits (9, 9 a or 9 b),that said ring (20, 20 a), or ring section (20 b), respectively,constitutes a component of an outer body (11, 11 a) which additionallyhas an upper part (21) or upper part section, respectively, and thatbetween an inner underside (15) of said outer body and an upper side(13, 13 a) of said inner body, a hot water distribution chamber (16) isleft free into which the hot water supply duct (17) opens which isdisposed in the upper part (21), or upper part section (21 b).
 10. Milkfroth generating device according to claim 9, characterized in that saidinner body (8 a, 8 b) and the ring (20 a) covering it, or the ringsection (20 b), respectively, are downwardly broadening truncatedcone-shaped, and that said outer hot water channels (9 a, 9 b) are alsoradially outwardly declined.
 11. Milk froth generating device accordingto claim 10, characterized in that said truncated cone-shaped inner body(8 a) and the outer body (11 b) covering it with a ring section (20 b),each, include an upper cylindrical section serving for easy removablefixation of said inner body in said outer body, said upper cylindricalsection being provided with fixation elements, particularly a thread(29) which is shaped on inner body (20 b) as an external threadpenetrated by sections of said hot water channel slits (29 b).
 12. Milkfroth generating device according to claim 10, characterized in thatsaid truncated cone-shaped inner body includes a band which fits into aninner ring groove in said truncated cone-shaped ring into which saidinner body can be inserted, and that said inner body and/or the ringconsist of elastic material so that the inner body is force-lockingly,though manually releasably, supported in the ring.
 13. Milk frothgenerating device according to claim 9, characterized in that a sieve(19) is disposed in said hot water sprayer head (1, 1 a, 1 b), betweensaid hot water distribution chamber (16, 16 a) and said hot waterchannels (9, 9 a, 9 b, 12).
 14. Milk froth generating device accordingto claim 13, characterized in that said sieve (19) is supported betweenan internal flange (23) in the upper part (21) and at least one spacerformed out from the upper side of said inner body (8, 8 a, 8 b). 15.Milk froth generating device according to claim 13, characterized inthat said pot-shaped outer body (11, 11 a) consists of said upper part(21) and a cylindrical section of ring (20, 20 a) screwed into it, whichis solidly connected with said inner body (8, 8 a), that from said upperpart (21), said internal flange is formed out which has an externalthread, and that in one upper cylindrical section of ring (20, 20 a) aninternal thread (22) is provided which can be screwed into the externalthread on said internal flange (23).
 16. Milk froth generating deviceaccording to claim 15, characterized by a sealing ring (26) between saidupper part (21) and said ring (20, 20 a) in a screwed-together state.17. Milk froth generating device according to claim 1, characterized inthat said froth generating device consists of poorly thermo-conductivematerial.
 18. Milk froth generating device according to claim 17,characterized in that the insert consists of Neoprene.
 19. Coffeemachine, particularly espresso machine, comprising a water heater and ahot water pressure generator as well as a milk froth generating deviceaccording to one of claims 2, 3 through 18, characterized in that as thehot water pressure generator and the water heater of said milk frothgenerating device, the hot water pressure generator and the water heaterof the coffee machine are used which are connected via said hot watersupply (17) with said hot water sprayer head.